Eggs have long been regarded for their nutrient density, providing consumers with a high-quality protein source in addition to a wide variety of critical minerals, vitamins, and trace elements.¹  Compared to other significant sources of dietary proteins, eggs provide relatively high levels of folate, biotin, choline, and vitamin A for a relatively small number of calories, and also deliver an impressive combination of amino acids.^2,3  Additionally, eggs serve as an affordable protein and nutrient source. As reported in the Nutrient Rich Foods Index, and again in a review by Iannotti et al. in 2014, eggs are the most affordable protein source in the United States when included as part of a comprehensive food list.^4,5 

However, despite the wide acceptance that eggs are an affordable and nutrient-rich food, the American public has been reticent to accept eggs as part of a healthy eating pattern owing to concerns about cholesterol intake. In fact, recent studies examining consumer data from the National Health and Nutrition Examination Survey (NHANES) found that from 2001 to 2012 the overall proportion of the U.S. population who consumed eggs regularly (21–22%; p = 0.311) remained unchanged.⁶  Research examining consumer perceptions about eggs and the barriers to their consumption found that egg consumption has declined owing to the perceived association most consumers make between the consumption of eggs and dietary cholesterol.^7–9 

While the perception that egg consumption is associated with dietary cholesterol and, therefore, is associated with increased levels of plasma cholesterol has been supported by recommendations put forth by the U.S. government and reputable public health organizations in the past, recent examinations of the body of literature concerning egg consumption suggest that eggs should be considered a healthy part of the diet. In the following sections, we will discuss the history of dietary recommendations that resulted in the long-held belief that egg consumption should be undertaken in moderation, the changes in the American dietary pattern that occurred as a result of those recommendations, several of the potential health benefits associated with eggs that make them a key part of the modern healthy dietary pattern, as well as the potential for eggs to be enriched in order to even better serve as a component of healthy diets.

Dietary recommendations concerning the consumption of eggs have been part of the public's understanding of nutrition for nearly half a century, dating back to the 1968 recommendation from the American Heart Association (AHA) that individuals limit their intake of dietary cholesterol to no more than 300 mg per day in order to reduce their risk of cardiovascular disease (CVD), and that individuals consume no more than three whole eggs per week in order to meet that recommendation.¹⁰  That recommendation created a paradigm shift in the way the American public viewed the consumption of eggs, providing the average consumer with an easy to understand dietary intervention they could undertake in order to improve their lifestyle, and resulted in an overall decline in the per capita consumption of eggs in the years that followed.¹¹  This recommendation against the consumption of dietary cholesterol, and eggs in particular, persisted for decades.

Dietary recommendations in the United States took their first form in a report published by the American Heart Association in 1957 that posited, in somewhat uncertain terms, that the changing diet of the average American may have contributed to the increased pathogenesis of atherosclerosis in the United States.¹²  As noted by Kritchevsky in The Journal of Nutrition, the American Heart Association released another report four years later in 1961 which focused on dietary fats and their relationship to heart attacks and strokes, putting forth recommendations for dietary modifications that began modeling the current construction of our modern dietary recommendations.^13,14  Seven years later, in 1968, the American Heart Association put forth a report that set the standard for dietary cholesterol and egg consumption that would persist for decades – that Americans should limit dietary cholesterol to no more than 300 mg per day and should not consume more than three egg yolks per week.¹⁰ 

Less than a decade after the American Heart Association recommended that consumers limit their dietary intake of eggs in order to achieve a dietary pattern that protected them against CVD, the United States government began the process of establishing federally sanctioned dietary guidelines for every United States citizen. The first iteration of these guidelines was created and published in 1977 by the U.S. Senate Select Committee on Nutrition and Human Needs, which mirrored the American Heart Association recommendation of limiting dietary cholesterol to 300 mg per day and suggested that Americans limit their intake of eggs as a means of achieving that goal.¹⁵  Following the publication of the report from the U.S. Select Committee on Nutrition and Human Needs, the federal government took steps to formalize the process of creating and disseminating dietary recommendations to the American public and established the Dietary Guidelines for Americans, which have been issued twice a decade since 1980 and provide citizens of the United States with recommendations for developing a healthful diet.

In 1980, the U.S. Department of Agriculture and the U.S. Department of Health and Human Services published the first edition of the Dietary Guidelines for Americans (DGA). These 1980 guidelines, published as a 19-page pamphlet, provided Americans with seven focus areas for improving their overall health through nutrition.¹⁶  One of these focus areas, “Avoid Too Much Fat, Saturated Fat, and Cholesterol,” encouraged Americans to limit their intake of dietary cholesterol in order to reduce their risk of CVD, and provided eggs as an example of a common food that consumers could moderate in their diet to achieve that goal. Recommendations that encouraged Americans to reduce their dietary cholesterol intake, specifically through a reduction in their consumption of eggs, appeared almost universally in the bidecennial DGA reports published by the federal government up to, and including, the report published in 2010.^17–22  A summary of the dietary recommendations for egg consumption and cholesterol included in each of the Dietary Guidelines reports can be found in Table 1.1.

In 2013, the American Heart Association published a report providing lifestyle management guidance for individuals aiming to reduce their risk of developing cardiovascular disease. This report included evidence-based recommendations for dietary patterns that were intended to reduce risk factors for CVD, including the reduction of low-density lipoprotein cholesterol (LDL-C). In the report, the AHA stated there was “insufficient evidence to determine whether lowering dietary cholesterol reduced LDL-C.”²³  This recommendation was the inverse of the dietary recommendation that the AHA and other reputable public health organizations had been making for decades, and represented a turning point in the way public health advocates, the United States federal government, and health researchers would talk about dietary cholesterol to the general public.

In 2015, amidst a growing consensus that claims concerning dietary cholesterol levels and their relationship to CVD and blood lipid levels had been overstated, the Dietary Guidelines revised their recommendation for dietary cholesterol and stated that there was not enough evidence to develop a quantitative limit for dietary cholesterol.²⁴  The 2015 Dietary Guidelines went on to say that more research was needed to determine what, if any, dose–response relationship existed between dietary cholesterol and blood lipid levels.²⁴  While this departure from decades' worth of dietary recommendations that instructed consumers to limit their intake of eggs was certainly notable to researchers and public health officials, it is unclear whether the change in recommendation has been effectively communicated to consumers and the general public.

Over the past five decades, the United States federal government, along with a large number of non-profits focused on consumer health, have advocated that individuals make a concerted effort to reduce their dietary intake of cholesterol by decreasing the number of eggs they consume over the course of an average day or week. However, with the release of the 2015 DGA, those recommendations have shifted away from discouraging individuals from incorporating eggs into their dietary pattern and have instead suggested that eggs can be a key part of a healthful diet. As this shift in dietary recommendations takes place, it is important to understand that the dietary recommendations concerning egg consumption that had persisted for half a century may have dramatically altered the American dietary pattern. Furthermore, the persistence of the dietary recommendation that consumers avoid consuming or over-consuming eggs may have created difficult-to-overcome information barriers that will make it less likely that consumers will incorporate eggs into what they perceive as a healthy diet.

A great deal of research has been done to study the consumption trends of eggs in the United States, helping researchers and policy makers to better understand how many Americans are regularly consuming eggs and to what degree. As reported by Wang et al. in 1996, early United States Department of Agriculture (USDA) data demonstrated that the average per capita consumption of eggs in the United States steadily declined over the course of the final four decades of the 1900s, dropping from 321 eggs in 1960 to 229 eggs in 1993.²⁵  More recent research examining the prevalence of egg consumption throughout the United States found that roughly 20% of the population consumed eggs on any given day.²⁶  This estimate, that one in five Americans consume eggs on any given day, represents a largely unchanged prevalence in egg consumption compared to similar research that examined the prevalence of egg consumption from 1988 to 1994.²⁷  The trend for annual egg consumption from 1960 to 2017, adjusted on a per capita basis, can be seen in Figure 1.1.

Dietary patterns in the United States are often varied when sociodemographic indicators are examined, including an individual's level of education, their age or income level, or their socioeconomic status.^6,28,29  Owing to the relative affordability of eggs compared to other high-quality proteins available to consumers, one might expect that the presence of markers for lower socioeconomic status might be associated with a per capita egg consumption that was higher than average.³⁰  Surprisingly, the odds of egg consumption in the United States population were not impacted by multiple measures of socioeconomic status, such as level of food security, participation in the Supplemental Nutrition Assistance Program (SNAP), or individual income.⁶  However, data analysis from 2003 to 2006 has indicated that the incorporation of eggs into the diet was critical for key nutrient contributions to women who were overweight and obese, and to individuals belonging to minority race or ethnic groups.^6,31,32  Taken together, this data suggests that public health workers, medical practitioners, and public health agencies must find new and effective ways to communicate the potential health benefits, and relative affordability, of eggs to populations who may be the most reliant upon them to meet their nutrient needs.

Following the decline of egg consumption in the United States in the latter half of the 20th century, some investigators questioned what had motivated Americans to reduce the number of eggs they were incorporating in their diet. Several researchers posited that the dietary recommendations that had been put forth by the American Heart Association, the DGA during the 1970s, 1980s, and 1990s, and by other public health organizations, had created a sense amongst the American public that eggs were an unhealthy food and should be avoided. In 1990, Brown and Schrader investigated how information concerning the link between cholesterol and eggs impacted per capita consumption of eggs in the United States and found that information linking eggs and cholesterol had resulted in 16% to 25% decreased per capita egg consumption by the first quarter of 1987.³³ 

The theory that the public's perception of eggs as an unhealthy food, specifically owing to their association with cholesterol, had impacted U.S. egg consumption was again tested in 1996 by Wang et al. By examining consumer survey data from the USDA and applying a double-hurdle model of analysis, researchers determined that health concerns about cholesterol were a significant factor that affected a consumers decision about whether to purchase and consume eggs.²⁵  The perception that eggs should not be considered part of a healthy dietary pattern but should instead be viewed as a risky food that individuals should avoid if possible has continued well into the 21st century. As noted by Kummerow in 2015, the cholesterol hypothesis has persisted as part of America's understanding about food and has resulted in Americans consuming fewer eggs per capita in 2011 than in 1945 as members of the medical establishment avoid recommending eggs as a healthy protein source for their patients.³⁴  With the recent changes to the dietary recommendations noted above, and the understanding that beliefs about eggs and cholesterol that we now consider to be outdated are a significant barrier to their consumption, it will be critical that public health officials and medical practitioners are able to adequately and clearly explain this shift in dietary principles to the public and to their patients.

As dietary recommendations continued to discourage Americans from viewing eggs as part of a healthy dietary pattern and to reduce the number of eggs they were consuming, a growing number of researchers began to question the strength of the scientific data that had led to such recommendations in the first place. As noted by Fernandez and Calle in 2010, the initial recommendation of limiting dietary cholesterol to 300 mg day⁻¹ for healthy individuals had little basis in scientific evidence and put the United States in the position of being one of the only nations proscribing an upper limit for dietary cholesterol to its citizens.³⁵  As researchers tested the strength of the association between dietary cholesterol consumption and human health, the body of scientific literature undermining the claim that Americans should actively limit their intake of dietary cholesterol grew, and eventually resulted in both the American Heart Association and the DGA reversing their stance on dietary cholesterol and removing recommendations for egg restriction from their guidelines.^23,24 

Despite early recommendations that egg consumption should be restricted because increased dietary cholesterol was related to an elevated risk of CVD, the preponderance of epidemiological data that has been published subsequently does not support the claim that such an association exists.^36,37  While many epidemiological studies have been conducted in order to test the proposed relationship between egg consumption and the risk of cardiovascular disease, one of the classical epidemiological studies to do so utilized the National Nurses' Health Study dataset. This study used data collected from 37 851 men between the ages of 40 and 75 at onset and 80 082 women aged 34 to 59 at onset. Researchers identified and documented 866 cases of coronary heart disease (CHD) and 258 incident cases of stroke in men, and 939 cases of CHD and 563 incident cases of stroke in women during the 8 year follow-up period of the study. After researchers made adjustments for age, smoking, and other known CHD risk factors, they found no evidence of a significant association between consuming eggs and risk of CHD or stroke in either men or women.³⁸ 

Additional classical epidemiological studies that sought to test the relationship between egg consumption and the risk of cardiovascular disease include the Framingham Heart Study and the NHANES data set, both of which concluded that dietary cholesterol provided by eggs in the diet had no relationship to the development of CHD.^27,39  Additionally, while some large-scale research studies have found that consumption of dietary cholesterol is associated with elevated LDL-C concentrations, Fernandez and Calle noted in 2010 that it is important to understand that for those individuals who do present a hypercholesterolemic response to dietary cholesterol, the increases are often observed in both the plasma LDL-C and the plasma high-density lipoprotein cholesterol (HDL-C) concentrations, which does not result in an altered LDL-C : HDL-C ratio.³⁵ 

Taken together, the findings from these epidemiological research studies would suggest that a public health recommendation that associates dietary cholesterol with blood cholesterol levels, or with an elevated risk of CVD, would be ill-advised. Moreover, these findings indicate that an incredibly common dietary belief that is well known to the general public, that consuming egg raises your cholesterol levels and is bad for your heart, is likely a claim without merit. These conclusions are further supported by clinical research investigating the relationship between dietary cholesterol and risk for CHD and chronic disease in the subsequent section.

In addition to multiple large-scale epidemiological studies that have demonstrated no connection between the intake of dietary cholesterol and the prevalence of CHD events, scores of clinical trials have been conducted to test the same hypothesis. One recent study conducted by DiMarco et al. examined the effect of increased egg consumption on plasma cholesterol levels in a healthy population.⁴⁰  The study observed 38 subjects, 19 men and 19 women, who participated in a 14-week crossover intervention where subjects consumed either 0, 1, 2, or 3 eggs per day for a controlled period of time. At the completion of the intervention, the researchers found that increased consumption of eggs was associated with an increase in HDL-C (p < 0.01) and decreased LDL-c (p < 0.05), and dose-dependent increases in plasma choline were also observed (p < 0.0001).⁴⁰  Not only do such findings suggest that the consumption of eggs is not associated with an increased risk of CHD, but findings of elevated HDL-C and increased plasma choline levels would also be considered positive health outcomes that may be beneficial to consumers.

One intervention study conducted in 2004 focused on the effects of dietary cholesterol on biomarkers for chronic disease in adolescents. The study included 54 children between the ages of 8 and 12, 29 girls and 25 boys, who participated in a crossover intervention that included one egg intervention period of two whole eggs per day, and one period that included the equivalent amount of egg whites. At the completion of the trial, biomarkers were analyzed and it was found that of the 54 children who participated in the study only 18 experienced a significant elevation in their plasma cholesterol levels.⁴¹  Notably, those 18 children who saw an increase in plasma cholesterol saw increases in both their HDL-C and LDL-C, with no significant changes in their LDL : HDL ratio. Of the 54 children who participated in the study, 36 had no significant change in plasma cholesterol at all.⁴¹  These findings further suggest that, for most individuals, dietary cholesterol plays little to no role in the regulation of plasma cholesterol and that for individuals who are affected by dietary cholesterol the observed changes are not likely to increase their risk factor for CVD because their LDL : HDL ratio remains unchanged.

Intervention studies have also been conducted in the elderly population to determine if individuals over 60 years of age would be more susceptible to changes in their plasma cholesterol levels based on their consumption of dietary cholesterol. One such study evaluated 42 elderly subjects, 29 postmenopausal women and 13 men, who were all free of diabetes and heart disease, and did not use reductase inhibitors. A crossover intervention was implemented that included a 1-month egg period where three large eggs were consumed per day and an intervention period where the equivalent amount of fat-free, cholesterol-free egg substitute was consumed.⁴²  At the completion of the trial the subjects' LDL-C and HDL-C concentrations were measured, and researchers determined that, while individual responses to the egg intervention varied amongst the participants, no alterations were observed in LDL : HDL ratios or in total cholesterol : HDL ratios. These findings suggest that dietary cholesterol, specifically the dietary cholesterol delivered through the consumption of eggs, does not result in an increased risk for heart disease in otherwise healthy elderly individuals.⁴² 

Intervention studies have repeatedly found that the consumption of dietary cholesterol is not associated with an increased risk for CVD and is not associated with detrimental changes in an individual's plasma cholesterol levels. The studies noted above demonstrate that this is true across age groups and genders. In fact, some intervention studies have even found that egg consumption is positively associated with increases in HDL-C, an outcome that would be considered healthful for many consumers. Much like the epidemiological data discussed earlier, human intervention studies would also suggest that public health claims advising against the consumption of eggs due to concerns about CVD risks and cholesterol levels were misguided.

Following decades of research that questioned the credibility of a dietary recommendation that instructed consumers to limit their daily intake of dietary cholesterol in order to maintain health, the growing scientific consensus supported a shifting away from such recommendations and instead beginning to inform consumers about the potential health benefits associated with the consumption of eggs.⁴³  As noted earlier in this chapter, amidst this growing consensus the U.S. federal government along with consumer health advocacy groups throughout the United States began to relax their recommendations concerning dietary restrictions for eggs and removed specific calls for consumers to limit eggs in their diet.^23,24,44 

While rolling back recommendations for consumers to avoid the consumption of eggs owing to a lack of scientific evidence to support such a claim is certainly a step in the right direction, it is incumbent upon public health officials to now rectify the decades of misinformation that they have perpetuated through their dietary recommendations. The need for aggressive correction in the public perception of eggs as an unhealthy food is especially important because, as discussed in the following section, eggs provide a myriad of health benefits, including high-quality protein, choline, and help with satiety.

Eggs have long been recognized for their nutrient density but were not thought of as part of a healthful dietary pattern owing to the common perception that consuming eggs was linked to increased cholesterol levels and, therefore, increased risk of cardiovascular disease.²  However, as dietary recommendations change and the public perception of eggs alters, it is important for health experts to understand the scope of nutritional health benefits offered by eggs when they are incorporated into the diet. Eggs provide a wide variety of nutrients, acting as an excellent source of protein and delivering a rich diversity of vitamins, minerals, and fats. A brief summary of some of the key nutrients provided by whole eggs, or egg whites, can be seen in Table 1.2, which is drawn from the USDA Nutrient Database for Standard ref. 45.

Adequate protein consumption for individuals is an area of high concern for health professionals and is essential for an individual's overall health and wellness. The international recommendation for dietary protein intake established by the World Health Organization is 0.83 g kg⁻¹ day⁻¹ for the average individual, with higher intakes recommended for high activity athletes, children, and the elderly.^46–48  One of the most important factors to take into account when considering eggs as a source of protein is their relative affordability compared to other protein sources of similar quality, making them a critical dietary component for low-income individuals who are trying to establish a healthy dietary pattern.⁴⁹  This is especially important as the quality of egg protein is considered to be perfect when using the protein digestibility-corrected amino acid score (PDCAAS) for protein quality evaluation. Using the PDCAAS method to evaluate the quality of proteins, a score of less than 1 indicates the presence of a limiting amino acid, or rather, that at least one of the nine essential amino acid is not present in large enough quantities to meet consumer needs.^50,51  When compared to other proteins that are considered to be of high quality, eggs have robust scores on the PDCAAS scale, performing nearly as well as meat and fish, and outperforming soy and wheat.^5,50  The high quality of egg protein and its relative affordability suggest that it is a logical food for public health officials to recommend to consumers who are seeking to build a healthful diet on a reasonable budget.

One of the key biochemical uses of ingested protein is the synthesis of muscle, with the increased consumption of high-quality protein being associated with improved synthesis of skeletal muscle tissue as well as with muscle repair and maintenance.⁵²  Specific to eggs, the high quantity of the essential amino acid leucine has been associated with increased gains in muscle tissue mass and, therefore, in strength and power.⁵³  Research done by Moore et al. looked specifically at egg protein consumption in healthy young male subjects found a dose–dependent relationship between the quantity of egg protein consumed and muscle protein synthesis.⁵⁴  The association between increased protein consumption and improved muscle maintenance has also been observed in elderly populations for whom sarcopenia, or the loss of muscle tissue, is an area of concern.^47,55  This research suggests that eggs should not only be viewed as a protein source to be utilized by individuals with financial concerns, but that their high-quality and highly digestible protein should be recommended for athletes concerned with muscle development and for ageing individuals who are seeking to develop healthful diets that will help them maintain adequate muscle function in their later years. In these cases, while it may not be critical that eggs are more affordable than other sources of high-quality protein, it would certainly remain a benefit for consumers.

In addition to its association with improved muscle synthesis and muscle maintenance, protein consumption has also been positively associated with increased levels of satiety.^56,57  Dietary strategies aimed at improving post-prandial satiety response have been recognized as a critical tool for public health workers as increased levels of satiety following the consumption of a meal have been associated with an overall daily decrease in caloric intake.⁵⁸  Satiety levels have been positively associated with the levels of protein, water, and fiber found within foods, suggesting that eggs may serve as a beneficial component of meals that are designed with the aim of increasing the satiety response in consumers.⁵⁹  In fact, using a common index comparing satiety responses to specific foods, it was observed that the satiety response following egg consumption was 50% greater than the satiety response associated with a common ready-to-eat breakfast cereal or that of white bread.⁶⁰  This would suggest that as public health workers, medical practitioners, and dietitians work with individuals on putting together meal plans aimed at assisting in weight loss, breakfast plans that include eggs may be more effective and healthful options than breakfasts where cereal grains act as the staple.

One study, conducted by Vander Wal et al., tested the ability of an egg-based breakfast to provide satiety to consumers when compared to a bagel breakfast. Both meals were matched for total energy and energy density. 125 men and women between the ages of 25 and 60 were assigned to one of four treatments: an egg breakfast, an egg breakfast plus a restricted calorie diet, a bagel breakfast, and a bagel breakfast plus a restricted calorie diet. After a 5 week intervention period, researchers found that the egg breakfast plus diet group had a 61% greater reduction in BMI (p < 0.05), a 34% greater reduction in waist circumference (p < 0.06), and a 65% greater reduction in weight loss (p < 0.05) when compared to the bagel plus diet group.⁶¹  While no significant difference was observed between the standard egg breakfast group and the standard bagel breakfast group, the findings of this study suggest that incorporating eggs into the dietary pattern of individuals who are seeking to manage their weight may be an effective dietary intervention.⁶¹ 

Another study, also completed by Vander Wal et al., examined the effect that eggs had on satiety in overweight and obese individuals.⁶²  Thirty women between the ages of 25 to 60 years with BMIs greater than or equal to 25 kg m⁻² participated in a randomized crossover study to test the effect an egg breakfast had on satiety when compared to a bagel breakfast. Subjects were fed one of the two treatments for breakfast and were provided a lunch 3.5 hours later. Satiety was also measured through self-reported questionnaires. Researchers in this study found that when participants consumed the egg breakfast they experienced greater feelings of satiety compared to the bagel breakfast, and also consumed significantly less energy (p < 0.0001) during their lunch.⁶²  This data also supports the belief that incorporating eggs in a consumer's dietary pattern is not only healthful but can also help individuals better manage their energy intake through increased satiation.⁶² 

It is clear from the research discussed above that the incorporation of eggs into meals can serve as an effective way for consumers to improve their satiety response, which may, in turn, help them limit their overall consumption of calories throughout the day. Certainly, a common question that medical practitioners and dietitians are repeatedly faced with is how to help patients in their quest to lose or manage their weight. The ability to recommend simple dietary changes, like choosing an egg breakfast rather than a bagel breakfast, could be an effective tool to help patients reach their health goals for weight management.

An essential micronutrient that has long been associated with eggs is choline.⁶³  Eggs are quite rich in choline, with higher choline levels than most other common foods. A comparison of choline levels between eggs and other common foods can be seen in Figure 1.2.⁶⁴  Choline must be obtained in the human diet and is critical in cellular methylation reactions that are important for gene expression and the development of the neurotransmitter acetylcholine.^65,66  Not only has choline deficiency been associated with the development of non-alcoholic fatty liver disease and with neural tube defects during pregnancy, but recent epidemiological and intervention studies have suggested that maternal choline intake during pregnancy is associated with a child's cognition later in life.^66–68  In addition to its role in neurological development, choline plays a critical role in the metabolism of lipids within the body. Choline has been found to promote very low-density lipoprotein hepatic secretion and has been shown to play a role in the prevention of hepatic steatosis.^9,69 

In addition to the well-documented physiological need for choline for proper fetal development, recent research has begun to investigate if improved choline intake during pregnancy is actually associated with improved cognitive outcomes in children. One recent study tested the relationship between the level of maternal choline intake during various stages of pregnancy and the cognitive abilities of offspring as they matured. Researchers examined choline intake during pregnancy in 895 mothers participating in Project Viva and then tested the children of those mothers when the children reached the age of 7 years to determine visual memory and intelligence scores. Researchers found that an association existed between increased choline intake by the mother in the second trimester and improved cognitive scores in the child.⁶⁸  The association between choline intake during the first trimester and improved cognitive scores amongst children was also observed, but to a lesser degree.⁶⁸  While additional research is clearly required to test this potential association before it is communicated to consumers in an authoritative manner, it would certainly be of benefit for health care professionals to know that encouraging the consumption of foods high in choline during pregnancy may actually provide added benefits for the children of patients.

Despite the relative affordability and accessibility of eggs, and their ability to deliver high amounts of choline into the diet, many individuals in the United States are still susceptible to inadequate choline intake. In fact, one 2017 study that examined the NHANES datasets from 2009 to 2014, and the additional NHANES datasets for pregnant women from 2005 to 2014, found that across genders, life stages, and even in pregnancy, individuals in the United States were susceptible to suboptimal intakes of choline.⁶⁶  However, the same study found that individuals who regularly consumed eggs had nearly double the usual intake of choline compared to individuals who did not consume eggs. Researchers for the study posited that it would be incredibly difficult for individuals who do not consume eggs or did not take a choline-containing dietary supplement to achieve the suggested adequate intake levels for their life stage.⁶⁶ 

As the recognition that eggs are part of a healthful dietary pattern continues to increase, it is ever more likely that researchers will continue to explore new ways through which the nutrient content of eggs can be improved. Whether these improvements are made through biotechnology, modified raising conditions for laying hens, or changes in the diet of laying hens, egg producers will seek to implement new best practices that will enhance both the nutrient density and desirability of their product.

Vitamin D is a critical nutrient for human vertebrates and is utilized by the body for the proper maintenance of serum calcium homeostasis.⁷⁰  The failure to achieve adequate levels of vitamin D, either through sunlight-dependent synthesis or consumption in the diet, has been connected to the development of rickets in young children and with the development of osteoporosis in grown adults.⁷¹  Both conditions are connected to the inability for bones to properly mineralize without adequate amounts of vitamin D. Rickets is associated with growth retardation in children, deformities of the skeletal system, weakness of muscles, and, in some cases, seizures.⁷²  Osteoporosis, diagnosed in adults, is characterized by exceptionally low bone mass and a related increase risk of bone fractures.⁷³  It is widely accepted by health officials that the general public is failing to attain serum vitamin D levels that are required for healthy function, and they have therefore deemed vitamin D to be a nutrient of concern for public health.⁷⁴  As public health officials seek to address the prevalence of vitamin D insufficiency, dietary interventions involving eggs, which contain reasonable amounts of vitamin D, have been of interest.

Eggs, specifically egg yolks, contain both the D₃ and 25(OH)D₃ forms of vitamin D and are a strong candidate for increased vitamin D fortification because vitamin D provided to laying hens in their feed is easily transferred to the egg yolk, which may allow farmers to increase vitamin D concentrations in eggs through simple modifications to feed.^75,76  In recent studies, researchers have experimented with chicken feed containing various amounts of vitamin D₃ and 25(OH)D₃ to test whether supplementing feed will actually result in eggs that have consistently higher concentrations of available vitamin D for the humans that consume them. One study, conducted by Browning and Cowieson, compared nine separate treatments of an ad libitum mash diet, with vitamin D₃ levels ranging from 2500 IU kg⁻¹ to 10 000 IU kg⁻¹, and 25(OH)D₃ levels ranging from 0 IU kg⁻¹ to 2760 IU kg⁻¹.⁷⁶  After nine weeks of consuming the experimental diets, hens' eggs were analyzed for D₃ and 25(OH)D₃ and it was determined that a strong dose–dependent relationship existed between D₃ and 25(OH)D₃ levels in the diets of laying hens and the D₃ and 25(OH)D₃ levels in the yolks of the eggs that were actually laid.⁷⁶ 

In addition to increasing the vitamin D levels of hen eggs through dietary supplementation, researchers have found that is it possible to increase the vitamin D levels of eggs by allowing laying hens to have greater access to the outdoors, thus stimulating sunlight-dependent synthesis of vitamin D. In 2014, Kühn et al. found that hens that had access to both indoor and outdoor habitats had a three- to four-fold increase in vitamin D₃ levels in their eggs compared to hens that were kept exclusively indoors.⁷⁷  Levels of vitamin D₃ in eggs reached even greater levels when laying hens were housed in exclusively outdoor environments.⁷⁷ 

As public health officials and governmental agencies work to educate consumers about the potential health benefits of eggs, producers will seek to find new ways to differentiate their products or make them more attractive to consumers. As vitamin D is a nutrient of concern, and evidence suggests there are multiple ways in which egg producers can improve vitamin D content in their eggs, eggs could be well positioned to assume the role of a staple source of vitamin D in the human dietary pattern.

Over 50 years ago, the United States federal government and consumer health advocacy groups initiated an information campaign that was intended to help the average consumer make healthier dietary choices by restricting their consumption of dietary cholesterol. This initiative, focused largely on providing the average consumer with easy to understand dietary guidance through the DGA, gave consumers the simple instruction to limit the number of eggs they consumed in an average week in order to maintain heart health and reduce their risk of CVD. These recommendations were made largely without scientific basis but were readily adopted by the general public throughout the United States and resulted in a precipitous decline in the overall purchase and consumption of eggs in the general population.

In the decades following these dietary recommendations, public health researchers throughout the county conducted countless epidemiological studies and clinical trials to test the relationship between the consumption of dietary cholesterol and increases in lipid and cholesterol markers associated with CVD. These studies overwhelmingly rejected the notion that dietary cholesterol was associated with plasma cholesterol levels and also found that when dietary cholesterol did impact plasma cholesterol levels, the ratio between LDL and HDL was largely unchanged. These findings resulted in a shift away from recommending restrictions in the consumption of eggs for the general population. However, the long timeframe for which dietary recommendations discouraging the use eggs existed and the relative simplicity of the dietary recommendation have already made the belief that eggs are not a healthful food nearly ubiquitous in the United States population.

Unfortunately, as noted in several studies aimed at gauging consumer attitudes towards eggs and individual willingness to purchase and consume them, the idea that eggs are linked to cholesterol levels has served as a significant deterrent for large portions of the population. This is troubling not only because the scientific community now agrees that such information is flawed, but also because eggs are able to play a critical role in the development of a healthful diet for much of the population. Not only are eggs affordable, but they provide an excellent source of protein to consumers, are rich in vitamin B12 and folate, and are high in choline.

While the public health efforts that encouraged Americans to avoid the consumption of eggs in the first place were certainly well-intentioned, the results of those recommendations over the course of the past 60 years should serve as an important lesson for individuals tasked with providing health information to the public. By telling consumers to avoid eggs for over half a century, public health officials have created large barriers to the consumption of a food we now agree is healthful, affordable, and important in a healthy dietary pattern. Not only does additional research need to be conducted that continues to demonstrate the health benefits of egg consumption, but new tactics need to be adopted for informing the public that egg consumption does not need to be restricted to ensure consumers are well informed of this dramatic change in dietary recommendations.